Thank you for your response. I am on Chapter 6 as mentioned next to the link you provided. What i understand is that the HTML mail is coded and mailed separately.
The do's and don't for coding are very well explained in the document.
I still have question regarding the Subscribe link in many websites, where one has option to subscribe through email, or the RSS.
1) When a user clicks on either of those, how and where is the response generated? (where are the client emails stored?)
2) The chapter doesn't talk about the RSS. How is it different from the HTML mail?
3) Is there a way to notify, that the subscriber read the content provided?